Outdoor Dispersion

The accurate prediction of the spread of dangerous substances is important for scenarios that help in preparing for possible attacks, as well as in the analysis and damage assessment that follows an event.

Fluent's experience with predicting outdoor dispersion events include:

• Exhaust plumes from ships, cars and factories
• Smoke columns that result from shipboard fires
• Gas leaks from ships, storage tanks and factories
• Urban neighborhood air flow and pollution dispersion
• Chemical warfare cloud engulfing a battle tank

Both Fluent and our clients have made efforts to quantify the accuracy of CFD predictions. These efforts have covered a spectrum of topologies ranging from atmospheric boundary layers over flat terrain (Project Prairie Grass field trial), via atmospheric flows over obstacle arrays (MUST, Mock Urban Setting Test), to flows through urban topologies and street canyons. In the latter category, our clients and/or Fluent have predicted the spread of a tracer gas released as part of the Urban 2000 study near Madison Square Garden in New York City and replicated the urban dispersion observed during the Joint Urban 2003 Field Campaign in Oklahoma City.

More recently, with the rising concern about terrorist attacks, Fluent's software has been used to predict the spread of particulates that resulted from the collapse of the Twin Towers and to predict the plume concentration associated with the release of a radioactive cloud.

The two plots above are comparisons of mean velocity and gas concentration profiles between CFD simulations with several mesh sizes and the measured data from the MUST field program. This program involved the release of a neutrally buoyant gas in an array of 120 containers.

Contours of pollutant concentration on a plane perpendicular to the wind in downtown Manhattan on September 11, 2001
Courtesy of the EPA (validation efforts are ongoing)

Cloud of methane resulting from a leak on an oil industry ship
Courtesy of Aker Engineering

View animation
The spread of a plume from a smoke stack
Animation courtesy of Intelligent Light